1. Field of the Invention
The invention is directed to a process and an apparatus for the preparation of a foam-forming, free-flowing mixture from free-flowing components which are stored in supply areas, wherein before the components enter the mixing zone at least one of the components is loaded with gas by leading this component from the supply area to a gas loading area, by gassing it there and leading it back to the supply area again, whereby in the supply area a gas cushion is maintained and the gas that is required for gas loading is taken from this gas cushion.
2. Description of the Prior Art
In the preparation of foam from free-flowing components in particular polyurethane components, the gas level in the reaction mixture has a significant influence on the course of the reaction and on the subsequent properties of the foam.
According to published application DE-A No. 3,244,037 (U.S. Ser. No. 550,428, filed Nov. 10, 1983, now abandoned) and unpublished application DE-A No. 3,442,954 (U.S. Ser. No. 772,964, filed Sept. 5, 1985 now U.S. Pat. No. 4,933,115), the U.S. Ser. Nos. hereby incorporated by reference, the gas loading is carried out by means of an ejector mixer. In this process the gas, which is drawn in by the ejector mixer, may be taken from the gas cushion of the supply container directly. In the unpublished application the device i.e. in particular the gas loading unit, is structurally fitted into the whole of the installation in such a way that the section of pipe running from the gas loading unit to the supply container is so short and the size of the cross-section is so large that no loss of pressure occurs. This means that the gassed component should flow back into the supply container.
In installations which are already available and could be adapted to this technology, problems frequently occur, however, if the required connection on the supply container does not have a large cross-section, and/or it is not possible to effect retrofitting and safety retesting of the supply containers without interrupting production. This narrow cross-section leads to a loss of pressure which makes it impossible for the gas loading unit according to DE-A No. 3,442,954 to function properly.
An object of the present invention is to create a technology which can both be integrated without any problems into installations which are already available and which can also be used in new installations such that the other advantages afforded by DE-A No. 3,442,954 are retained. These advantages include the production of an extremely fine dispersion, freedom from losses of propellants and, in particular, the regenerative effect of the gas loading element.
The solution entails compressing the gas which is taken from the supply area to a higher pressure than the pressure in the gas loading area before it is dispersed into the desired component.
Because the gas is taken to a higher pressure level the pressure loss of the fluid component between the loading area and the supply area can be compensated for as desired. With this new process it is possible to integrate the gas loading unit described in DE-A No. 3,442,954 into the installation without any problems and while retaining all of the advantages especially the regeneration of the gas loading element.